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Preservative treatments & finishes

Like to know what wood to use building a pergola or framing a barn? How about the difference between tung oil and polyurethane as a floor finish? How to revive decking or deal with merbau stains? Or how to meet the building code or bushfire standards? Or ask about the environmental advantages of wood or forest certification?

Q. We have used wespine blue for our roof structure. Is it preferable to also use treated blue for the battens? And are there any issues fixing colorbond to blue pine?

You may be required to used treated timber for roof framing if you are building in a Restricted Movement Zone (RMZ) with respect to the European house borer. Maps showing the location of Restricted Movement Zones can be downloaded from the net at If you are in one of these zones, Wespine Blue is an accepted treatment against the borer (and other insects). If you are not in a declared RMZ, use of Wespine Blue will give you some reassurance against attack and may help to prevent the spread of the European House Borer, although perhaps not strictly required. There are no issues in fixing Colorbond roofing to Blue Pine. The difficulty in fixing Colorbond to treated timber arises when copper-based preservatives are used (CCA, ACQ, etc.) and moisture is present, since contact between dissimilar metals can cause enhanced corrosion.

Q. What would you recommend to seal jarrah railway sleepers with a smooth transparent finish so they can be used outdoors as garden furniture?

Transparent finishes on timber exposed to the weather are always a challenge, since they break down on exposure to UV and the eroding effect of rain. On a rough surface such as a railway sleeper the most practical finish will be decking oil or garden furniture oil, since it can be re-applied when necessary without much surface preparation. Varnishes tend to fail by cracking and peeling, and the surface needs to be sanded back before the coating can be renewed. This is not practical on a rough sawn surface. Perhaps you intend to sand the sleepers to a smooth surface, in which case a varnish that contains UV absorbers would be an option, as long as you are prepared to maintain it.

Q. I did a search on your site for "LOSP handrails" and found it should not be used externally for these applications? Our builder is using them now when the quote was for CCA.

CCA treatment has not been permitted for timber handrails since 2006 due to concerns about hand-to-mouth transfer of chemical, particularly in the case of small children. However, other copper-based preservatives such as ACQ are permitted. There have been concerns about the durability of LOSP-treated handrails, but rather than saying they should not be used we prefer to explain how they can be used to achieve a satisfactory life-span. A useful data sheet has been prepared by Timber Queensland that goes into this in more detail. It can be downloaded from this address: If you are unsure that these conditions can be met in your situation, you may wish to call for a treatment more suited to a high hazard, such as ACQ.

Q. Looking for a paint on solution that treated wood rot, then I fill it with epoxy.

There are many paint-on anti-rot treatments on the market, but we suggest one of the boron products. They are effective against wood rot but have low toxicity to humans. One such product is ProtecTimber and you can find more information if you write the product name in your browser. An anti-rot boron product is also available in the form of a solid stick to insert in the wood, marketed under the name "No-Rot". The stick dissolves when it gets damp and diffuses through the wood.

Q. Treatment for timber repair from rot. I got a product from Keiran O'Sullivan back in about '04 or 5 wondering whether it's still around ?

I'm afraid we need a bit more detail to answer your question. If you can find the name of the product you are seeking we might be able to help. Or if you can advise whether you are looking for an anti-rot treatment or a wood filler we could suggest an alternative.

Q. I have some newly installed timber veneered cabinetry in my kitchen and bathroom finished in '2-pac stain'. I find the surface of the veneer is rough where you can feel the open grain, and that dirt gets trapped in the grain leaving unsightly lines. Would this be expected for the described finish?

We weren't sure exactly what kind of finish has been applied to your cabinets. Stains, applied to timber to colour it, are intended to be sealed with a lacquer or varnish, particularly in wet areas. This is usually sufficient to fill the grain or at least smooth it out. For a really smooth surface, grain fillers are used but normally only for furniture. If the surface feels rough after application of varnish we suggest light sanding with fine sandpaper and then applying another coat of varnish.

Q. We are staining wenge wood. It is coming out blotchy. Is there something we can do or try so its not so blotchy.

We were surprised you wanted to stain wenge wood given that it's so dark to start with. However, you might find it stains more evenly if you wipe the stain on rather than brushing it on. Another technique is to seal the wood first, usually with sanding sealer or shellac. You will find lots of useful information on the net if you write "blotchy stain" in your browser.

Q. We are working on a new day spa in Gippsland which will be clad in cypress shiplap cladding. We also have a vertical timber screen of glulam - we have specified Glulam Durabeam Cypress GL10. The supplier of the Durabeam recommends that their product 'Cutek' is used as a protective coating, however this is a hydrocarbon oiled recoat which we have concerns with from an environmental perspective. Also the colour range of the Cutek is not what we are after. We would like to use one of the Quantum Timber Finishes, which are oil based products. Can you please advise if this would be suitable? The day spa will be exposed to harsh climatic conditions.

It's difficult to give advice on specific brand-name timber finishes since our organisation doesn't carry out exposure tests. Consequently we don't have any performance data unless we've used a product ourselves, or we know the history of a structure where it has been used. Quantum products sound OK and the testimonials on their website seem genuine, but we don't know any more about them than you do. Maybe you could ask Quantum if there is a building in your area where their products have been used, so you can see how they perform. It might also be helpful to download a copy of Technical Design Guide #13 from our sister website via this link: Its title is "Finishing Timber Externally".

Q. The issue is rain water collecting at the ground cement level, hence outer cover has rotted & further need a solution to the timber poles cracks above the ground level as well. Please find attached pictures which are self-explanatory of the issues which need to be tackled. Kindly let me know suitable treatments & product availability with relevant cost.

There's a good explanation on the net at this address where a homeowner used the WEST system (Wood Epoxy Saturation Technique) to repair rotted posts. Note the essential first step of removing decayed material and then treating the remaining sound timber with a fungicide such as copper naphthenate or a boron-based product. The other option is to cut the posts off at the bottom and mount them on metal brackets bolted to the concrete, with the timber itself clear of the concrete to allow ventilation.

Q. Not sure if you can help or direct me to where I can find helpful information. I am renovating an old home clad in red mahogany weatherboard. I am taking the paint off and would like to seal the timber to preserve its natural beauty rather than repaint. Oil will be high maintenance and cost prohibitive. I am curious are there any products which will do what I am after. Thinking of using a satin varnish? Cannot seem to find any forums for renovating red mahogany weatherboards.

The traditional weatherboard house was always painted, which allowed quite long maintenance intervals. Clear oils and varnishes have a shorter life than paint as they are more susceptible to ultraviolet attack. They are still a practical choice for relatively small areas, but perhaps a bit demanding when your whole house is clad in timber. When a natural look is desired, we feel the best compromise is to use a semi-transparent stain. These finishes achieve a longer life than clear oil and don't fail like a varnish by peeling. Note that this is general advice and we don't know how large your house is, whether it is one or two storeys, or what budget you are prepared to commit to maintenance. On a two storey house, it's usually desirable to use long-lasting finishes because of the greater difficulty of access. If you are really committed to a clear varnish finish, and your house is single-storey so there is easy access for maintenance, make sure to choose a varnish that contains UV absorbers, eg. Feast Watson Weatherproof Varnish. Sikkens products also have a good reputation but generally contain a light stain to increase maintenance intervals.


Did you know?

About 6% of Australia’s 147 million hectares of native forests are public forests potentially available for timber harvesting. Timber is harvested from about 1% of those public native forests each year.